* Vote expected to deliver comfortable yes to independence
* Kurds to use vote as mandate to engage in talks for secession
* Iran imposes flight ban, Turkey threatens retaliation
* Tension simmers over vote in disputed areas like oil-rich Kirkuk
* U.S. warned Kurds vote "provocative" and "destabilizing" (Adds comments against the vote, flashpoint oil city)
By Maher Chmaytelli and Michael Georgy
ERBIL/SULAIMANIYA, Iraq, Sept 25 (Reuters) - Voting began in northern Iraq on Monday in an independence referendum organised by Kurdish authorities, ignoring pressure from Baghdad, threats from neighouring Turkey and Iran, and international warnings it may ignite yet more regional conflict.
The vote, expected to deliver a comfortable "yes" for independence, is not binding. However, it is designed to give Massoud Barzani, who heads the Kurdistan Regional Government (KRG), a mandate to negotiate the secession of the oil producing region with Baghdad and neighbouring states.
For Iraqi Kurds - the largest ethnic group left stateless when the Ottoman empire collapsed a century ago - the referendum offers a historic opportunity despite the intense international pressure to call it off.
"We have seen worse, we have seen injustice, killings and blockades," said Talat, waiting to cast a vote in the regional capital of Erbil, as group of smiling women, in traditional colourful Kurdish dress, emerged from the school showing their fingers stained with ink, a sign that they voted.
The Kurds also say the vote acknowledges their crucial contribution in confronting Islamic State after it overwhelmed the Iraqi army in 2014 and seized control of a third of Iraq.
But with roughly 30 million ethnic Kurds scattered over international borders across the region, Tehran and Ankara fear the spread of separatism to their own Kurdish populations.
The U.S. State Department warned the KRG last week that "holding the referendum in disputed areas is particularly provocative and destabilizing."
The KRG is holding the referendum not only in the long-standing Kurdish autonomous region of Iraq, but also in wider areas in the north of the country into which its forces have advanced in the fight to defeat Islamic State. These areas also have large non-Kurdish populations.
The Turkish Foreign Ministry said Ankara did not recognise the referendum and would view its outcome as null and void, adding that the Iraqi Kurdish government was threatening the peace and stability of Iraq and the whole region.
Prime Minister Binali Yildirim said that his government was evaluating steps regarding its border gates with northern Iraq and air space in response to the vote.
Ankara would make decisions in more direct talks with the Iraqi central government after the referendum, adding that economic, political, diplomatic and military steps were being discussed, he said in an interview with Turkish broadcasters.
Ankara's forces are again fighting a Kurdish insurgency in Turkey following the collapse of a peace process.
Polling stations opened their doors at 8:00 a.m. (0500 GMT) and should close at 6:00 p.m. The final results should be announced within 72 hours.
The voting is open to all registered residents, Kurds and non-Kurds, in the Kurdish-held areas of northern Iraq aged 18 and over, according to the referendum commission.
The commission estimates the number of eligible voters at 5.2 million, including those living abroad and who started casting electronic ballots two days ago.
Voters should tick yes or no on the ballot asking them just one question in Kurdish, Turkish, Arabic and Assyrian: "do you want the Kurdistan Region and Kurdistani areas outside the (Kurdistan) Region to become an independent country?"
Iran declared a ban on direct flights to and from Kurdistan on Sunday, while Baghdad asked foreign countries to stop direct oil trading with autonomous region and demanded that the KRG hands over control of its international airports and border posts with Iran, Turkey and Syria.
Tehran supports Shi'ite groups who have been ruling or holding security and government positions in Iraq since the U.S.-led invasion which toppled Saddam Hussein in 2003.
Opposition to the vote simmered among non-Kurdish populations in areas disputed by the KRG and Baghdad, and mainly the multi-ethnic oil-rich region of Kirkuk.
"Iraq is against the Kurds, so are the Turks, the Iranians, the whole Arab region and Europe. They are going to live in a cage," said Mohammed Mahdi al-Bayati, a Shi'ite Turkmen and a local leader of the Iranian-backed Badr Organisation paramilitary group in Tuz Khurmato, south of Kirkuk.
In Sulaimaniya, a bastion for political groups opposed to Barzani, queues in front of the polling stations were shorter than those in Erbil, and there were fewer signs and billboards celebrating the referendum, reflecting resentment that a yes vote could be seen as a plebiscite for the Kurdish leader.
"I will not vote, the referendum is not good, it could be dangerous because of the threat from Turkey and Iran," said a shop owner of Sulaimaniya, Ali Ahmed.
Despite Turkey's threatened retaliation, it has so far kept the Kurdish oil export pipeline that crosses its territory open.
After World War One, the victorious powers Britain and France carved up the Ottoman empire leaving the Kurds scattered mainly over four countries: Iraq, Iran, Turkey and Syria.
All of them suffered persecution and were often denied the right to speak their language. Those in Iraq were uprooted under Saddam Hussein's regime and suffered an attack using chemical weapons.
Syria is embroiled in a devastating civil war and its Kurds are pressing ahead with their own self-determination. (Writing by Maher Chmaytelli; Additional reporting by Raya Jalabi and Ahmed Jadallah; Editing by Nick Macfie and David Stamp)
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